Acoustic Stethoscope



530m 27, 21945. h. F. OLSON ACOUSTIC STETHOSCOPE Filed Oct. 29, 1943 3Sheets-Sheet l 12.1.9 Olli-lill llil. .4 s

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5 Sheets-Sheet 2 Snnentor H. F. oLsoN ACOUSTIC STETHOSCOPE Filed oct.29, 1945 Nav. 27, 1945.

No?. 27, MM5

H. F. OLSQN ACOUSTIC STETHOSCOPE Filed Oct. 29, 1943 3 Sheets-Sheet 5 4o/ao law, 4000 FWEQUEMY .40@ -fawdwo :Snventor @MMA Patented Nov. 27, .Y19:15

, '2,389,863 ACOUSTIC srs'moscors Harry F. Olson, Princeton, N. J.,assignor to Radio Corporation of America, a corporation of Dela-Application October 29, 1943, Serial No. 508,215 s claims. (ci. isi- 24)This invention relates to an acoustic pickup device, and moreparticularly to an acoustic stethoscope, the present invention being anim- Drovement over that disclosed and claimed in my copendingapplication, Serial No. 437,139, filed April 1, 1942, now Patent No.2,363,686, granted November 28, 1944.

In the aforesaid application, I have disclosedY an acousticstethoscopewhich is effective over a much wider range than stethoscopesof the prior art and by means of which sound can be picked up over alocalized area of the subject being examined. The stethoscope comprises,briefly, a pickup device of relatively small area adapted to cooperatewith a portion of the subject having a relatively high impedance, thepickup device being coupled to a suitable detector, such as the ears ofthe user, by a tapered acoustical line which'matches the relatively highimpedance at the receiver to the relatively low impedance of the ears,thereby being capable of transmitting acoustical energy withoutsubstantial loss or attenuation.

While the wider frequency range afforded by the stethoscope disclosed inmy aforesaid copending application is a very desirable feature, thereare some cases in which this wider range causes some confusion becausethe added low and high frequency sounds occasionally mask certaindesired sounds upon which the user wishes to concentrate. The primaryobject of my present invention, therefore, is to provide an improvedstethoscope of this type which will not be subject to the aforementionedlimitation.

More particularly, it is an object of my present invention to provide animproved, wide range stethoscope by `means of which sounds of variousfrequencies can be readily differentiated.

Another object of my present invention is to provide, in a stethoscopeof the type set forth above, a corrective acoustic network by means ofwhich undesired portions of the frequency'range to which the stethoscopeis responsive may be eliminated without impairing the desired portion ofthis range.

It is also an object of my present invention to provide an improvedacoustic stethoscope and network as above set forth which is simple inconstruction, inexpensive in cost, and highly efficient in use.

In accordance with my present invention, I form in the tubularmemberconstituting the acoustic coupling device between the pickup andthe receiver a plurality of openings which are Aspaced from each otherand rotatably mount on this tubular member a second tubular memberformed with a plurality of discrete acoustic chambers. The secondtubular member is arranged to communicate with the passage in thetapered line through one` or more of the aforesaid openings whereby oneor more of the aforementioned chambers may be brought into communicationwith the passage in the tapered line. Each of the chambers and the airin the associated openings constitutes a, Helmholtz resonator whichoperates in known manner to reject or attenuate certain frequencies orbands of frequencies transmitted by the tapered line, and the secondnamed tubular member may be selectively rotated on the tubular member ofthe tapered line to any desired position for either attenuating the lowfrequencies, the high frequencies, both the low frequencies and the highfrequencies, certainintermediate frequencies, or any combination thereofas may be desired.

e The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best beunderstood from the following description of one embodiment thereof,when read in connection with the accompanying drawings, in which theacoustic system of the improved stethoscope of my present inventionshown applied to the body and the ear,

Figure 3 is a wiring diagram ofthe equivalent electrical circuit of theacoustic system shown in Figure 2,

Figures 4 to 7, inclusive, are sectional views of the acoustical networkof my present invention shown applied to a portion of the tubular memberconstituting the tapered line, and arranged in each gure to be effectiveover different fre quency ranges, and

Figures 4a to 7a, inclusive, are response curves showing, respectively,the responses of the arrangements of Figures 4 to 7.

Referring more particularly to the drawings, wherein similar referencecharacters designate corresponding parts throughout, Fig. 1 shows apickup device I adapted to be placed against the human body or othersubject to be studied and comprising a supporting plate 2 having ahollow stem 3 extending from its back face, a bore or opening beingformed in the supporting plate 2 in communication with .the hollow stem3. Secured tothe front face of the plate 2 is a backing member 1 havingan opening Sin communication with the opening 5 and also having aplurality of forwardly extending projections II thereon. The backingmember 1 may be of any suitable material, but it is preferably made ofan elastic material, such as rubber, in accordance with the teachings ofmy above identied patent. The projections II may be conical, pyramidal,or the like. A, membranous diaphragm I3 of thin, sheet rubber or thelike is carried by the supporting plate 2 with its rear or inner surfacelin engagement with the apices of the projections II. The projections IIare spaced from each other on the backing member 1 and are distributedover the entire area of the diaphragm I3, the spacing of the projectionsbeing such as to provide a plurality of intersecting andintercommunicating passageways I4 which communicate with the openings 9and 5 and the hollow stem 3. all as more fully described and claimed inmy above identified patent.

Fitted onto the stem 3 is a exible tube I5 of rubber or the like whichconnects the pickup device I to a tube I6, the latter, in turn, beingconnected to a Y connector I1. The connector I1 connects the tube I6 toa pair of ear tubes I9 terminating in a pair of ear pieces 2|.' Thetubular members I5 and I6 are provided with a continuously taperedpassage 23, 24 which expands gradually and uniformly from the stem 3 tothe connector I1. ear tubes I9 are formed with similarly expandingpassages 25 and 21 so that, from the stem 3 to the ear pieces 2|, acontinuously expanding passage is provided. Except for the addition ofthe patent, the tube I5 of the latter being connected,

directly to the Y connector I1 instead of through the tube I6.

The diaphragm I3 is of the order of 1" inv diameter and the relativelyhigh impedance of the area of the human body covered thereby when incontact therewith matches the surge acoustic impedance of the air in thestem of passageway 23 at its smaller or receiver end. Since, however,this does not match the impedance of the ear canals, the passages 23,24, 25, and 21 are tapered as above described, the rate of taper beingsuch that the relatively high impedance at the pickup end of the tube I5will be matched to the relatively low impedance of the ear canals at theear pieces 2|.

A stethoscope such as that described thus far has a frequency range offrom about 40 cycles per second to about 4000 cycles per second. Thisrange permits hearing sounds generated in the human body which cannot beheard with other stethoscopes. In some cases, the additional soundswhich are heard cause confusion by masking the sounds to which it isdesired to listen particularly. To avoid this diiculty, there may beformed in the wall of the tubular member I6 one or more openings whichaord communication between the portion 24 of the tapered passage and theexterior thereof. Two such openings 30 and 3|, spaced from each otherlongitudinally along the tube IS, a third opening 30a aligned with butspaced 180 from the opening 30, and a fourth opening 3|a aligned withbut spaced only 90 from the opening 3|, are shown by way ofillustration. Another tubular member The connector I1 and the 33 whichisclosed at each end and has a partition 35 therein dividing it into twochambers 34 and 36 is rotatably mounted on the tube I6 about theopenings 30,.30a, 3| and 3|a. The inner wall of the member 33, whichacts as a nlter device, is provided with a pair' of openings 31 and 33spaced from each other in a longitudinal direction the same distance asthe openingsl 30 and 3|, the opening 31 being arranged to cooperate withthe openings 30 and 30a, and the opening 36 being arranged to cooperatewith the openings 3| and 3|a.

The filter tube 33 may be manually rotated 90 on the tube I6 from oneposition wherein its inner wall closes off all of openings 30, 30a, 3|

and 3|a, as shown in Fig. 4, to a second position wherein the opening 31is brought into registration with the opening 30a, thereby establishingcommunication of the passage portion 24 with the larger chamber 34, theopenings 30, 3| and 3|a remaining closed off, as shown in Fig. 5. 1n theposition of Fig. 4, the filter is entirely ineffective and the taperedline transmits the full range of frequencies, as shown by the responsecurve of Fig. 4a. In the position of Fig. 5, however, the mass M1 of theair in the aligned openings 3Ila and 31 resonates with the capacitanceCin of the volume of air in the chamber 34 In: the well known manner ofa Helmholtz resonator, and if the size of the openings 30a and 31 andthe volume of the chamber 34 are properly chosen, the resonator willlter out the low frequency sounds, as shown by the curve of Fig. 5a,thereby preventing them from reaching the ears.

The filter tube 33 may also be rotated manually 90 more to a thirdposition, as shown in Fig. 6.

'In this position, the openings 30, 30a and 3| are closed off and theopening 38 is brought into registration with the opening 3Ia to therebyestablish communication between the passage portion 24 and the smallerchamber 36. The mass M2 of the air in the aligned openings 3|a and 33will then be free to resonate with the capacitance CA2 of the air in thechamber 36 to trap the high frequency sounds when properly dimensioned,and the resulting response will be of the type shown by the curve ofFig. 6a.

In a fourth position to which the filter tube 33 may be rotated anadditional 90, the openings 31 and 38 are both brought into registrationwith their respectively associated openings 3|) and 3|, as shown in Fig.7, the openings 30a and 3|a then being closed off. This will bring bothof the chambers 34 and 36 into communication with the tapered passageportion 24, and the two Helm` holtz resonators will then be effective toattenuate or filter out both the low irequencysounds and the highfrequency sounds to provide a response such as shown by the curve ofFig'. '7b. Thus, by a simple, manual manipulation, any one of theresponses represented by the curves of Figs. 4a. to 7a, inclusive, maybe obtained. The filter tube 33 may be releasably locked in any one ofthe adjusted positions shown in Figs. 4 to 7, inclusive, by suitablemeans (not shown).

Fig. 2 shows a simplified, acoustic system employing the lter device ofmy present invention in a stethoscope as above described, and Fig. 3shows a wiring diagram of the analogous electrical system or circuit. Inthese figures,

B represents the body under examination and in which a sound source Sgenerates acoustic vibrations with a pressure p,

Zas represents the impedance of the body B,

M represents the mass of the diaphragm I3,

Can represents the capacitance of the diaphragm,

Css represents the capacitance of the resilient projections Il,

CM represents the capacitance of the air chamber between the diaphragmi3 and the projections Il.

zu represents the impedance Csi represents the capacitance of the airchamber 3l,

M1 represents the mass of the air in the openings 30 or 30a, as the casemay be, and the opening 31 when aligned,

CA2 represents the capacitance of the air in chamber 36, and

Mz represents the mass of the air in the openings 3i or 3ia, as the casemay be, and the opening 33 when aligned.

When the filter tube 33 is placed in the position o1' Fig. 4, this isequivalent to opening the shunt Circuits Csi, M1 and CA2, M2 of Fig. 3.When the filter tube 33 is rotated to the position of Fig. 5, this isequivalent to closing the switch of the circuit CA: and M1. Turning thefilter tube 33 next to the position of Fig. 6 will be equivalent toopening the switch of the circuit Car, M1 and closing the switch of thecircuit CA2, Mz. Finally, when the filter tube 33 is turned to theposition of Fig. "I, this is equivalent to closing the switches of bothof the shunt circuits CM,

the

Mi and CA2. M2.

From the foregoing description, it will be apparent to those skilled inthe art that I have provided a simple and effective means for excludingundesired sounds in a wide range stethoscope without interfering in theslightest with the transmission of sounds in the desired range.Obviously, the filter tube 33 may be provided with as many chambers asmay be found suitable or desirable, two chambers having been illustratedmerely for the purpose of illustration. Moreover, it will undoubtedly beapparent to those skilled in the art that many variations of the presentinvention, as well as other changes in the particular one described, arepossible. I .therefore desire that my invention shall not be limitedexcept insofar as is made necessary by the prior art and by the spiritof the appended claims.

I claim as my invention:

l. In an acoustic stethoscope, a pick-up device having a relatively highimpedance equal substantially to that of a given area of a subject to beexamined, an acoustic coupling line connected at one end to said pick-updevice and adapted to be connected at its other end to a detector havinga relatively low impedance, said line including a tubular member andhaving a tapered passage between its ends which expands gradually fromsaid pick-up device to its detector end. the ends of said passage havingimpedances which match said high and low impedances, re-

spectively, whereby said coupling line is adapted 'to transmitacoustical energy from said subject to said detector without substantialattenuation,

said tubular member having a plurality of openings in the wall thereofwhich are spaced from each other and each of which affords communiof theear canals, o

cation between said passage and the exterior,A and means associated withsaid line for rejecting acoustical energy of certain frequencies withinthe range transmitted by said line whereby to prevent energy of saidcertain frequencies from reaching said detector, said rejecting meanscomprising a plurality of acoustical resonators of the Helmholtz typeequal in number to the number of said openings and each associated witha separate one of said openings whereby to afford cornmunication betweeneach of said resonators and said passage, said resonators each beingeffective over a different frequency range.

2. The invention set forth in claim 1 characterized by the inclusion ofmeans for selectively establishing communication between any one or moreof said resonators and said passage at will.

3. In an acoustic stethoscope, a pick-up device having a relatively highimpedance equal substantially to that of a. given area of a subject tobe examined, an acoustic coupling line connected at one end to saidpick-up device and adapted to be connected at its other end to adetector having a relatively low impedance, said line including atubular member and having a tapered passage between its ends whichexpands gradually from 4said pick-up device to its detector end, theends of said passage having impedances which match said high and lowimpedances, respectively, whereby said coupling line is adapted totransmit acoustical energy from said subject to said detector withoutsubstantial attenuation, said tubular member having a plurality ofopenings in the wall thereof which are spaced from each other and eachof which affords communication between said passage and the exterior,and means associated with said line for rejecting acoustical energy ofcertain frequencies within the range transmitted by said line whereby toprevent energy of said certain frequencies from reaching said detector,said rejecting means coml Aeffective over a different frequency range,and

said second tubular member being rotatable on said nrst-named tubularmember to any one of a plurality of predetermined positions whereincommunication between any one or more of said resonators and saidpassage may be established at will.

HARRY F. OLSON.

